1. Field of the Invention
This invention relates to radiographic imaging and more specifically to image data related to computed radiography (CR), digital radiography, and/or film-based radiography.
2. Description of Related Art
The use of photo-stimulable phosphor image storage screens as a replacement for X-ray film and other sensors is well known. Phosphor image screens work by trapping energy from individual X-ray photons in a storage layer, thus forming a latent image. The latent image can then be read by scanning the storage layer using a suitable wavelength excitation beam, typically from a focused laser. The excitation beam causes the screen to release the latent image in the form of emitted stimulable phosphor light that is proportional to the X-ray energy applied to the screen during exposure. The emitted light is collected by an optical system and is converted into an electronic signal proportional to the emitted light. The electrical signal is then converted into a digital value and passed to a computer that generates and stores an image file. The image file can then be displayed as a representation of the original radiograph, and manipulated with image enhancement software applied to augment the radiographic information.
The detection efficiency of a radiographic system is referred to as the Detective Quantum Efficiency, or DQE. Existing CR systems do not read out all of the energy stored in the latent image; this reduces the DQE of the system. If the readout efficiency, and thus the DQE, of CR systems can be improved, images of a given quality can be obtained using lower X-ray exposures to the patient. Conversely, for a given x-ray exposure to the patient, images of higher quality can be obtained.
The latent image is stored in a multiplicity of energy states; some of these are readily accessible using a single-wavelength readout beam. However, that same wavelength beam accesses states at other energy levels very inefficiently. Even if the power of the readout beam is significantly increased, much of the latent image will not be read out.